1. Field of Invention
Broadly, the present invention relates to the use of concrete as a material for constructing buildings, and more particularly to construction of buildings using precast panels of concrete. With still more particularity, the invention relates to the use of modular panels to make up at least a portion of the walls of buildings, the panels being precast of concrete comprising lightweight aggregates and strength enhancers.
2. Prior Art
Heretofore, precast panels for the construction of buildings, particularly for the walls thereof, have utilized structural concrete to attain the structural strength required to withstand handling loads and loads imposed by the building structure. However, the use of structural concrete, which normally comprises heavy aggregates such as gravel and the like, has caused the panels to be excessively heavy, so that handling the installation has been both expensive and laborious, also requiring unnecessarily expensive heavy handling equipment. Further, such panels have required much finishing work after installation into the building to provide the aesthetic effects often desired. Such panels have, additionally, been difficult to work with, since fastening building objects thereto requires the use of rock drills and the like. Further, they have often required the addition of insulating materials thereto. The resulting final building walls have accordingly been composite structures wherein the panels has comprised only one part, so that the total expense of such panels has seriously compromised the potential economic advantages inherent to mass produced panels.
In attempts to overcome the aforesaid disadvantages of the use of structural concrete for panels, much work has been done with lightweight aggregates in the concrete for use in panels. However, concrete made from these lightweight aggregates, which include vermiculite, perlite, scoria, pumice, expanded shale, cinders and others, have in most instances possessed less than desirable structural strength, or have even been excessively low in structural strength. Concretes comprising vermiculite and perlite in particular have largely been limited to strength below 1000 pounds per square inch so that their uses have largely been as insulating fillers, with other structural components being provided to carry the imposed loads. Concretes comprising pumice or scoria exhibit somewhat higher structural strengths, while being somewhat more dense. However, the strength of the pumice and scoria concretes have been largely limited to 1000 to 3000 p.s.i., still less than desirable for many structural uses.
Another problem with the use of lightweight aggregates comprising concrete for precast building panels is the tendency of such concretes to be pervious to water, so that exposed panels tend to be damaged by weather excessively fast. Thus, although a concrete comprising scoria, for example, as the principal aggregate may, marginally, possess sufficiently structural strength, such concrete is normally unacceptably susceptibile to moisture and water.
While expanded shale, clay, or slate can be used as a lightweight aggregate to produce acceptable structural strength while remaining sufficiently impervious to water, such concretes are comparatively expensive to construct, since these aggregates require extended drying in kilns and the like, or sintering, and careful handling of the aggregate, generally with specialized equipment, to achieve the requisite strengths.
Still another important consideration for modular panels making up the walls of buildings has been their insulating properties. Resistance to heat flow through the panels should be at a high level to minimize the cost of subsequent heating and cooling the resulting structure. Generally, the concretes exhibiting high strength have been less than desirable as insulating structures. Structural concrete, for instance, is not in itself an effective insulator for the wall of a building. Generally, even the above mentioned more expensive lightweight concretes fall short of desired insulating properties. Accordingly, insulating layers of other materials have of necessity been added to the panels used in the construction of buildings. These have often comprised cellular plastic materials, or even cork, wood and the like, and have contributed additional material and installation expense. Attempts have also been made to construct panels comprising layers of concrete for strength and layers for high insulative properties, the layers being cast one upon the other. However, these panels have often been unsatisfactory because the layers tend strongly to separate, before or after installation into a building, so that such panels often cannot be so used.